1. Field of the Invention
The present invention relates to an electromagnetic valve and, in particular, to an improvement in an electromagnetic valve of a normally closed type structured such that, when it is open with a coil energized, the area of a flow passage can be varied according as the fluid pressure of an inlet port is high or low.
2. Description of the Related Art
Conventionally, an electromagnetic valve of this type is already known in, for example, the following JP-A-2000-219118. In JP-A-2000-219118, between a master cylinder and the suction port of a pump, there is interposed an electromagnetic valve and, when the electromagnetic valve is opened with a coil energized, in case where no liquid pressure is output from the master cylinder, first and second valve mechanisms are opened to thereby increase the flow passage area and, in case where the liquid pressure is output from the master cylinder, the second valve mechanism is closed but the first valve mechanism is opened to thereby reduce the flow passage area.
By the way, movable seat members, which respectively constitute part of the first and second valve mechanisms, are structured so as to be movable with respect to each other in the axial direction thereof in the range where they are restricted with respect to a movable core; and, in case where the axial lines of the movable seat members are inclined with respect to the movable core and second valve, in the case of the above-mentioned conventional structure, there is a possibility that either the sitting seal performance between the first valve part and first valve seat or the sitting seal performance between the second valve part and second valve seat can be impaired.
The present invention aims at eliminating the above drawbacks found in the conventional electromagnetic valve. Accordingly, it is an object of the present invention to provide an electromagnetic valve which can prevent the axial lines of the movable seat members from inclining to thereby be able to positively maintain both of the sitting seal performance between the first valve part and first valve seat or the sitting seal performance between the second valve part and second valve seat.
In attaining the above object, according to the present invention as set forth in a first aspect, there is provided an electromagnetic valve having: a cylindrical-shaped valve housing including an outlet port in one end thereof and an inlet port in the side wall of the axial-direction middle portion thereof; a fixing core to be fixed to the valve housing so as to close the other end of the valve housing in a fluid-tight manner; a movable core stored in the valve housing so as to be opposed to the fixing core; a first return spring applying a spring force for moving the movable core so as to apart from the fixing core; a coil applying an electromagnetic force for attracting the movable core toward the fixing core in energized condition; and, first and second valve mechanisms respectively interposed between the inlet port and outlet port, the first valve mechanism including a movable seat member disposed opposed to the movable core on the opposite side of the fixing core so as to be moved in the axial direction thereof with respect to the movable core in a limited range, a second return spring for pushing the movable seat member to the side where the movable seat member is moved apart from the movable core, a first valve part disposed on the movable core within a valve chamber so formed in the interior of the valve housing as to be in communication with the inlet port, a first valve seat disposed on the movable seat member in such a manner that the first valve part is seated on the first valve seat, and a first valve hole formed in the movable seat member in such a manner that one end thereof is communicatable with the outlet port and the other end thereof is opened in the central portion of the first valve seat, the second valve mechanism including a cylindrical-shaped valve seat member fittable and fixable to one end side of the valve housing while forming the valve chamber between the movable core and itself, a second valve seat disposed on the valve seat member so as to be situated coaxially with the first valve seat and faces the valve chamber, a second valve hole formed in the valve seat member so as to be larger in diameter than the first valve hole, communicates with the outlet port and is opened in the central portion of the second valve seat, and a second valve part disposed on the outer periphery of the movable seat member so as to be seated on the second valve seat, wherein, on the movable seat member, there is integrally disposed a cylindrical-shaped guide part which, when the second valve part is seated on the second valve seat, is cut off from the valve chamber but, when the second valve part is separated from the second valve seat, forms an annular-shaped passage communicating with the valve chamber and is slidably fitted into the second valve hole; and, in the guide part, there is formed a communication passage for allowing the annular-shaped passage to communicate with the interior of the guide part.
According to the structure of the present invention as set forth in the first aspect, the movable seat member is guided by the guide part, which can be slidably fitted into the second valve hole, in such a manner that it is prevented from inclining with respect to the axial lines of the movable core and second valve seat, thereby being able to prevent the axial line of the movable seat member from inclining, which makes it possible to maintain positively not only the sitting seal performance between the first valve part and first valve seat but also the sitting seal performance between the second valve part and second valve seat. Also, in a state where the second valve part is rises up or is separated from the second valve seat and the second valve mechanism is thereby opened, there can be secured a flow passage which communicates from the valve chamber through the annular-shaped passage, communication passage and the interior of the guide part to the outlet port.
Also, according to the present invention as set forth in a second aspect, in addition to the structure of the present invention as set forth in the first aspect, an annular-shaped vacuum pressure chamber, which is situated between the second valve seat and annular-shaped passage while the second valve part is seated on the second valve seat, is formed between the inner surface of the second valve hole and the outer surface of the movable seat member in such a manner that pressure receive area thereof facing the movable seat member on the second valve seat side is set larger than pressure receive area thereof facing the movable seat member on the annular-shaped passage side; and, in the movable seat member, there is formed a communication hole for allowing the annular-shaped vacuum pressure chamber to communicate with the intermediate portion of the first valve hole. According to the present structure, a state, in which the first valve mechanism is open and the second valve mechanism is closed, can be maintained more positively. That is, the state, where the first valve mechanism is open and the second valve mechanism is closed, is maintained due to generation of a fluid pressure force which, due to a pressure difference between the fluid pressure on the valve chamber side and the fluid pressure on the outlet port side lower than the fluid pressure on the valve chamber side, presses the movable seat member toward the side where the second valve part can be seated on the second valve seat; but, in case where a pressure difference between the fluid pressure on the valve chamber and the fluid pressure on the outlet port side is small, there is a possibility that the closed state of the second valve mechanism cannot be maintained. However, since the fluid is sucked out from the annular-shaped vacuum pressure chamber through the communication hole to the first valve hole side as the fluid flows through the first valve hole, there can be generated a vacuum pressure force which attracts the movable seat member to the side where the second valve part can be seated on the second valve seat; and, therefore, even in case where the pressure difference between the fluid pressure on the valve chamber side and the fluid pressure on the outlet port side is small, the closed state of the second valve mechanism can be maintained more positively.